This disclosure generally relates to marine vibrators for use in acquiring seismic data.
Seismic surveying is used for identifying subterranean elements, such as hydrocarbon reservoirs, freshwater aquifers, gas injection zones, and so forth. In seismic surveying, seismic sources are placed at various locations on a land surface or sea floor, with the seismic sources activated to generate seismic waves directed into a subterranean structure. Seismic data signals are typically acquired by measuring and recording data during a land or marine seismic survey. A land seismic survey may be performed by repeatedly firing a seismic energy source at the surface of the earth and recording the received signals at a set of sensors or receivers. Similarly, a marine seismic survey may be performed by repeatedly firing a seismic energy source (e.g., air-guns, dynamite, marine vibrators or the like) into the sea or at the seafloor and recording the received signals at a set of receivers.
In a towed marine seismic survey, the receivers are typically disposed on seismic streamers and the source is disposed on a seismic source array. Both, the seismic streamers and the seismic source array, may be towed across the sea by a vessel. The sensors may typically be laterally displaced at regular intervals along the seismic streamers. However, there may be situations where a non-regular distribution of the sensors may be preferred or where the source array and the streamers may be positioned at different depth levels.
During the marine seismic survey, the cycle of firing the source and recording the received signals may be repeated a plurality of times. Vibroseis is a seismic method in which a vibrator is used as an energy source to generate a controlled wavetrain. A marine vibrator is an instrument which produces mechanical oscillations and may be used as a seismic source for vibroseis. As such, during a seismic survey, the marine vibrator applies a periodic vibration of continuously varying frequencies into the surrounding medium during a sweep period typically lasting several seconds.
Marine vibrators are large mechanical structures that include moving parts to generate the desired vibrations. A common source of failure with conventional marine vibrators is the seals disposed between moving and stationary parts of the vibrator. Such seals are commonly placed adjacent to the water interface with the vibrator, thus leading to undesirable wear and tear that reduces the reliability of the vibrator.